pdf № 348, December

DOI: 10.19110/geov.2023.12.1

The Upper Pechora basin is part of the northeastrn margin of the European Platform. In the Paleozoic, it was located within the carbonate shelf of the passive continental margin. According to A. I. Eliseev, Visean terrrigenous-carbonate (platamovy type) and Upper Visean-Lower Artinskian carbonate (kaleydovy type) formations occupy the upper part of the final sedimentation cycle of the formations row. According to new data, the history of the geological development of the Upper Pechora basin of the Late Visean-Asselian period has significant differences. Four types can be distinguished in the structure of sediments according to the composition of rocks: siliceous-clay-limestone, limestone, dolomite-limestone, siliceous-limestone. They were formed during three stages respective to the time of formation of three transgressive-regressive cyclites: the Visean-Serpukhovian, Bashkirian-Moscovian, Upper Carboniferous-Lower Permian. The studied deposits are divided into lithological complexes: siliceous-clay-carbonate of open sea (Tulian), siliceous-carbonate of open sea (Aleksinian-Early Mikhailovian, Bashkirian-Early Moscovian, Kasimovian-Midle Gzhelian), carbonate of shallow-shallow (Late Mikhailovian-Protvinian, Moscovian), and also the Late Gzhelian-Asselian shallow-depression (siliceous-limestone, limestone, clay-limestone). Lithological complexes, formed in open-sea conditions, belong to formations from the platamovy type and in shallow-shallow conditions — to formations from the kaleidovy type (by Eliseev, 2008).

Keywords: geological formations, carbonate deposits, Lower Carboniferous — Lower Permian, Northern Urals.

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DOI: 10.19110/geov.2023.12.2

The object of the study is the carbonate section «Pacha-Lasta» (Ilych river, Northern Urals). The work is based on the study of the composition, structure of rocks and species diversity of the foraminifera contained in them. The rocks are represented by various limestones with numerous remains of foraminifera, brachiopods, corals, echinoderms, frequent calcispheres and rare stromatolites. Based on the presence in the complex of certain foraminifera genera Biseriella, Globivalvulina, various Eostaffella (including E. ikensis tenebrosa) as well as the species Endothyranopsis sphaerica and Asteroarchaediscus baschkiricus, the Venusian age of the deposits is reliably established. Stromatolite formations, which are not characteristic of the same-age deposits of the area, were established at two intervals of the studied section. They are composed of micritized colonies of cyanobacteria, among which Ortonella and Girvanella are identified. These formations belong to the type of skeletal stromatolites, which in the Silurian and Late Devonian had a certain paleogeographic position and fixed the margin of the carbonate platform. For the Ilych River basin, a consistent decrease in relative sea level is assumed after the Early Visean transgression with a change in the conditions of the open sublittoral (Tula and Aleksinsky horizons) to the conditions of insular shallow water (Mikhailovsky and Venevsky horizons). In the latter, stromatolites can sometines occur, which are not characteristic of the Upper Visean deposits of the area.

Keywords: stratigraphy, paleogeography, foraminifera, stromatolites, Visean, Northern Urals.

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DOI: 10.19110/geov.2023.12.3

The paper presents the results of macroscopic and microscopic study of Riphean stromatolites of the Pavyuga Formation from a new locality on the left bank of the Vorykva River (Middle Timan). The stromatolites form a stromatolite bioherm. The microstructure of the stromatolite assemblages is characterised by layering of different composition and granularity; traces of organogenic formations of clotted and filamentous type were found in microgranular interlayers. Numerous traces of secondary transformations, such as pyritization, dolomitization on shells, and fenestra formation, were noted. The taxonomic affiliation of the stromatolites to the species Gimnosolen sp. and Inseria djejimi Raab. allows dating to the Late Riphean. A similar association is known from the upper part of the Pavyuga Formation, but the colonies of stromatolites are orientated disorderly in that association, which indicates the environment of the organogenic buildup margins.

Keywords: Stromatolithes, Bystrinsk Group, correlation, microbial structure, Middle Timan.

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DOI: 10.19110/geov.2023.12.4

The trachytes of the Tsilemsky Kamen of Middle Timan are rocks of the Shoshonitic series. The rocks have a microporphyry structure with a bostonite groundmass. Trachytes contain two varieties of potassium feldspar. The laths of the groundmass are composed of igneous sanidine, and the small grains along the edges of subisometric late quartz segregations are composed of hydrothermal microcline. Dating of trachytes by the K-Ar method gave an age of 365±8 Ma; the intrusion of the alkaline dike occurred in the Late Devonian. These rocks, along with trap basalts, recorded the occurrence of several pulses of plume magmatism on Timan in Devonian time.

Keywords: Middle Timan, trachytes, K-Ar age, plume.

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DOI: 10.19110/geov.2023.12.5

This article shows the role of dynamic non–hydrostatic pressure forces and viscous stresses in asthenosphere of tectonically active transition zones from the continent to the ocean. We have studied zones of active tectonic processes in the lithosphere and the underlying mantle, affecting the lithospheric blocks, the day surface of the Earth and the boundaries of density inhomogeneities. We showed the predominant influence of viscous stresses on the formation of mantle diapers and often associated hydrocarbon deposits. In subduction zones, in which a large-scale descending convective flow descends into the upper mantle as a sinking hard lithospheric block. We studied forces that determine the angle of subduction, depending on the age of the lithosphere, the rate of subduction and the rheological properties of the mantle material. We applied the method of analytical thermodynamic modeling of the tectonic structure of the upper mantle (lithosphere, asthenosphere) in the transition zone from the continent to the ocean. We concluded that the relative role of dynamic pressure forces prevailed in zones characterized by horizontally elongated asthenospheric movements in the mantle, as it happened under extended oceanic lithospheric plates. The novelty of the research is connected with the conclusion that under lithospheric micro-plates and near their boundaries, the roles of dynamic pressure forces and viscous stresses are comparable. In the areas of thermal diapirs associated with subduction zones and often located in transition zones from the continent to the ocean, the role of viscous stresses prevails. Thermal diapirs in subduction zones sometimes lead to the formation of hydrocarbon deposits due to mantle degassing processes.

Keywords: dynamic pressure forces, viscous stresses, «continent—ocean» transition zones, thermal diapers, oil and gas potential.

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DOI: 10.19110/geov.2023.12.6

We carried out the analytical oxidation of kerogen samples from oil shales of Ordovician kukersite from the Baltic region, Domanik shales from Timan-Pechora and Upper Jurassic oil shales of the Kashpir deposit by potassium permanganate in an alkaline medium. We performed a single-stage oxidation with 3.5 % solution of potassium permanganate, followed by analysis of trimethylsilyl derivatives of carboxylic acids using chromatography-mass spectrometry, and multi-stage oxidation by 0.5 % solution of potassium permanganate and analysis of oxidation products using IR spectroscopy. Some n-alkyl structures are peripherally associated with the kerogen matrix in the kerogen of Domanik and Jurassic shales, while in the structure of kukersite kerogen, n-alkyl structures are mainly connecting links for larger fragments. Milder, in case of a multi-stage process, oxidation results in formation of large fragments of kerogen, generally repeating its carbon structure, but more oxidized.

Keywords: kerogen, oil shales, oxidation by potassium permanganate, structure of organic matter, IR spectroscopy, carboxylic and dicarboxylic acids.

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